This short review summarizes 4 main reasons for which low-fat diets are preferred to limit excessive weight gain: (1) For metabolic reasons, fat intake does not measurably stimulate fat oxidation; dietary fat above energy requirements is stored in adipose tissue. (2) Diets that are high in fat or are energy dense have a weak satiating effect and promote a passive overconsumption of energy relative to need. (3) A recent meta-analysis on the effect on body weight loss of low-fat diets followed for >2 months showed a significant weight difference of 3.3 kg between the diet and the control groups. A low-fat diet may also be beneficial in helping maintain weight loss. (4) Low-fat diets are also advocated to lower the risk of coronary heart disease and certain forms of cancer. There is no evidence showing that the small physiologic reduction of plasma highdensity lipoprotein cholesterol levels with a low-fat diet is detrimental.